Add 'command id' field to messages

This allows for correlating response messages to the command message that
caused them.

js/main.ts

@@ -11,10 +11,19 @@ import { assert } from "./util";
 const globalEval = eval;
 const window = globalEval("this");
 
-function startMsg(): ArrayBuffer {
+let cmdIdCounter = 0;
+function assignCmdId(): number {
+  // TODO(piscisaureus) Safely re-use so they don't overflow.
+  const cmdId = ++cmdIdCounter;
+  assert(cmdId < 2 ** 32, "cmdId overflow");
+  return cmdId;
+}
+
+function startMsg(cmdId: number): ArrayBuffer {
   const builder = new flatbuffers.Builder();
   const msg = fbs.Start.createStart(builder, 0);
   fbs.Base.startBase(builder);
+  fbs.Base.addCmdId(builder, cmdId);
   fbs.Base.addMsg(builder, msg);
   fbs.Base.addMsgType(builder, fbs.Any.Start);
   builder.finish(fbs.Base.endBase(builder));
@@ -27,7 +36,8 @@ window["denoMain"] = () => {
   // First we send an empty "Start" message to let the privlaged side know we
   // are ready. The response should be a "StartRes" message containing the CLI
   // argv and other info.
-  const res = deno.send(startMsg());
+  const cmdId = assignCmdId();
+  const res = deno.send(startMsg(cmdId));
 
   // TODO(ry) Remove this conditional once main.rs gets up to speed.
   if (res == null) {
@@ -39,6 +49,7 @@ window["denoMain"] = () => {
   // Deserialize res into startResMsg.
   const bb = new flatbuffers.ByteBuffer(new Uint8Array(res));
   const base = fbs.Base.getRootAsBase(bb);
+  assert(base.cmdId() === cmdId);
   assert(fbs.Any.StartRes === base.msgType());
   const startResMsg = new fbs.StartRes();
   assert(base.msg(startResMsg) != null);

src/handlers.h

@@ -3,7 +3,9 @@
 #ifndef HANDLERS_H_
 #define HANDLERS_H_
 extern "C" {
-void handle_code_fetch(const char* module_specifier,
+#include <stdint.h>
+
+void handle_code_fetch(uint32_t cmd_id, const char* module_specifier,
                        const char* containing_file);
 }
 #endif  // HANDLERS_H_

src/handlers.rs

@@ -17,6 +17,7 @@ fn test_example() {
 
 #[no_mangle]
 pub extern "C" fn handle_code_fetch(
+    cmd_id: u32,
     module_specifier: *const c_char,
     containing_file: *const c_char,
 ) {
@@ -24,8 +25,10 @@ pub extern "C" fn handle_code_fetch(
     let containing_file = string_from_ptr(containing_file);
 
     println!(
-        "handle_code_fetch. module_specifier = {} containing_file = {}",
+        "handle_code_fetch. cmd_id = {} module_specifier = {} containing_file = {}",
-        module_specifier, containing_file
+        cmd_id,
+        module_specifier,
+        containing_file
     );
 
     unimplemented!();

src/main.cc

@@ -22,7 +22,7 @@ static char** global_argv;
 static int global_argc;
 
 // Sends StartRes message
-void HandleStart(Deno* d) {
+void HandleStart(Deno* d, uint32_t cmd_id) {
   flatbuffers::FlatBufferBuilder builder;
 
   char cwdbuf[1024];
@@ -37,20 +37,20 @@ void HandleStart(Deno* d) {
 
   auto start_argv = builder.CreateVector(args);
   auto start_msg = CreateStartRes(builder, start_cwd, start_argv);
-  auto base = CreateBase(builder, 0, Any_StartRes, start_msg.Union());
+  auto base = CreateBase(builder, cmd_id, 0, Any_StartRes, start_msg.Union());
   builder.Finish(base);
   deno_buf bufout{reinterpret_cast<const char*>(builder.GetBufferPointer()),
                   builder.GetSize()};
   deno_set_response(d, bufout);
 }
 
-void HandleCodeFetch(Deno* d, const CodeFetch* msg) {
+void HandleCodeFetch(Deno* d, uint32_t cmd_id, const CodeFetch* msg) {
   auto module_specifier = msg->module_specifier()->c_str();
   auto containing_file = msg->containing_file()->c_str();
   printf("HandleCodeFetch module_specifier = %s containing_file = %s\n",
          module_specifier, containing_file);
   // Call into rust.
-  handle_code_fetch(module_specifier, containing_file);
+  handle_code_fetch(cmd_id, module_specifier, containing_file);
 }
 
 void MessagesFromJS(Deno* d, deno_buf buf) {
@@ -59,17 +59,18 @@ void MessagesFromJS(Deno* d, deno_buf buf) {
   DCHECK(verifier.VerifyBuffer<Base>());
 
   auto base = flatbuffers::GetRoot<Base>(buf.data);
+  auto cmd_id = base->cmdId();
   auto msg_type = base->msg_type();
   const char* msg_type_name = EnumNamesAny()[msg_type];
-  printf("MessagesFromJS msg_type = %d, msg_type_name = %s\n", msg_type,
+  printf("MessagesFromJS cmd_id = %d, msg_type = %d, msg_type_name = %s\n",
-         msg_type_name);
+         cmd_id, msg_type, msg_type_name);
   switch (msg_type) {
     case Any_Start:
-      HandleStart(d);
+      HandleStart(d, base->cmdId());
       break;
 
     case Any_CodeFetch:
-      HandleCodeFetch(d, base->msg_as_CodeFetch());
+      HandleCodeFetch(d, base->cmdId(), base->msg_as_CodeFetch());
       break;
 
     case Any_NONE:

src/msg.fbs

@@ -18,6 +18,7 @@ union Any {
 }
 
 table Base {
+  cmdId: uint32;
   error: string;
   msg: Any;
 }